The present invention relates to a system for assembling a tube in a connecting element, a process for assembling a tube in a connecting element and a housing for a braking assistance servomotor in a braking control device including such a system.
Braking devices in motor vehicles conventionally comprise an assistance servomotor permitting the generation of an operating pressure in a master-cylinder without making an operator working the brake pedal bear the whole of the necessary thrust effort. The servomotor comprises a rigid casing or housing separated in tight manner into two chambers by a mobile partition, the said partition being firmly attached to a composite piston placed between the master-cylinder and an operating rod connected to the brake pedal and controlling the opening of a valve to vary the pressure in the chambers. The housing of the servomotor, generally formed of a front casing and a back casing is assembled in tight manner with the master-cylinder and the whole is assembled by the said housing to a vertical wall of the motor vehicle.
When the operator operates the brake pedal, the housing is subjected to high pressures and to a large reaction force, proportional to the force obtained at the outlet of the master-cylinder. To avoid the housing becoming deformed or detaching from the vertical wall of the vehicle, a first technology consists of using housings made of thick sheet metal. A second technology consists of providing the housing with tie rods or reinforcement elements, attached by their ends to the bottoms of the front and back casings, which are opposite each other, by means of connecting pieces. Each reinforcement element can consist of a solid or hollow tube. In the latter case, assembly of the master-cylinder and the housing can be effected by means of fixing screws passing in the hollow tubes. One of the ends of the tube comprises for example a thread and is screwed onto a so-called back fixing piece crimped around a fixing hole of the back casing. The other end of the tube is inserted in a bore in a so-called front fixing piece, also crimped around a fixing hole in the front casing, the said end being in abutment against a shoulder in the said bore.
To provide for assembly and tightness between the tube and the front fixing piece, U.S. Pat. No. 5,487,327 proposes, as shown diagrammatically in FIG. 1A, to simultaneously crimp the fixing piece 200 onto the front casing 201 and the tube 202 onto the fixing piece by providing a knurling 203 on the end of the tube inserted in the bore 204 provided with a shoulder 205. In a modified embodiment, the crimping of the tube is obtained or finished by flattening down a collar of the connecting piece in an annular groove present on the outer surface of the tube. This assembly system involves a crimping operation using large forces which require solid tubes. Moreover, this crimping operation must be carried out in a very precise manner to avoid damaging the tube.
With reference to FIG. 1B, international application WO 99/41122 describes another assembly system in which the tightness between the tube 206 and the fixing element 207 is obtained by the presence of an O-ring seal 208 placed in an annular groove 209 in the bore 210. This assembly system requires the presence of an additional piece.
The aim of the present invention is to propose an alternative to the two assembly systems described above, which is simple to produce.
The invention proposes a system for assembly of a tube with a female connecting element comprising a longitudinal bore provided with a transversal shoulder, in which system a hollow end portion of the tube is inserted into the said bore in abutment against its shoulder, characterised by the fact that the longitudinal wall of the said end portion comprises a zone deformed by compression between the said shoulder and the remainder of the tube and transversally deformed within the internal wall of the bore to ensure mechanical connection and tightness between the tube and the connecting element.
In accordance with one characteristic, the longitudinal wall of the end portion comprises a zone of lesser thickness.
Advantageously, the longitudinal wall of lesser thickness extends from the free end of the end portion to a transversal shoulder present inside the tube.
In accordance with another characteristic, the bore passes right through and includes two cylindrical portions separated by its shoulder, a first portion having a small cross-section smaller than the external cross-section of the tube and a second portion having a large cross-section substantially equal to or greater than the external cross-section of the tube, so that the hollow end portion of the tube is inserted in the second portion.
Advantageously, the tube is hollow through the whole of its length.
In accordance with another characteristic, the second portion has a length greater than that of the said end portion, so that the deformed zone of the end portion is closer to the shoulder in the bore than the free end of the second portion.
In accordance with a modified embodiment, the second portion has, in the vicinity of its shoulder, an annular groove extending transversally outwardly to at least partially receive the deformed zone.
In accordance with another modification, the longitudinal wall of the second portion of the bore includes knurling at least at the level of the deformed zone of the tube.
A further aim of the present invention is to propose a process for assembling a tube with a female connecting element.
The process for assembling a tube with a female connecting element comprising a bore provided with a shoulder is characterised by the fact that it comprises:
the introduction into the said bore of an end portion of the tube, the said tube being hollow along the said end portion, the said hollow end portion forming or comprising a zone of weakness having a lesser resistance to compression than the remainder of the tube, until the free end of the end portion abuts against the said shoulder, and
the application of a compression force to the said tube, substantially along the bore axis, greater than the resistance to compression of the said zone of weakness, so as to deform the latter transversally outwardly and form a deformed zoned ensuring mechanical connection and tightness between the tube and the connecting element.
In accordance with one characteristic, the process comprises the introduction into the said bore of an end portion of the tube, the zone of weakness of which consists of a thinner zone of lesser thickness than the remainder of the tube, formed by a reduction of thickness inside the end portion.
In accordance with another characteristic, the thinner zone extends over a determined length from the free end of the end portion.
In accordance with a modification, the process consists of applying a compression force until the zone of weakness is deformed and at least partially pressed back into an annular groove in the bore extending transversally in the vicinity of the shoulder.
A further aim of the present invention is to propose an hermetic housing for a braking assistance servomotor including such a system.
The hermetic housing in accordance with the invention including two casings, reinforcement elements formed of tubes assembled by their ends, by means of connecting elements, with opposed walls of the casings, is characterised by the fact that the tubes are assembled with the connecting elements in accordance with the assembly system defined above.
Advantageously, the hermetic housing comprises connecting rods inserted through the connecting elements and tubes and intended to permit assembly of the breaking device with a wall of the vehicle for which the braking device is intended.